Vegetable and Field Crops 203 



may remain alive for many years. The disease may be car- 

 ried to adjacent fields by insects, also by the means sug- 

 gested under soil diseases. There is little or no danger of 

 disease carriage by the seed. 



Since onion sets are immune, the effects of the smut can 

 be avoided by sowing seed in soil that is free of disease and 

 then transplanting into the field. With this mode of onion 

 culture the only difficulty is to secure plats free from in- 

 festation, and this is not often a serious one. In extreme 

 cases disinfection of the soil in plats may be resorted to. 

 (See soil disinfection, p. 460.) On farms once infested all 

 refuse (screenings, tops of infected sets) should be collected 

 and burned to reduce the amount of spores. Where soil, 

 known to be infested, is to be planted, formalin (1 ounce in 

 1 gallon of water) should be used and applied with a drip 

 attachment on a seed drill in the proportion of one gallon 

 of solution for each 1200 linear feet of row. 



Ground quicklime or stone lime, better the former, ap- 

 plied at the rate of 75 to 125 bushels per acre on the freshly 

 prepared soil just before seeding, has been useful. If ap- 

 plied by drill, harrowing will not be required; if broadcast, 

 harrowing should precede planting. One hundred pounds of 

 sulfur mixed with fifty pounds of air-slaked Hme applied in 

 the drills is also effective. 



These methods used separately or combined are suffi- 

 ciently established to warrant general use on smutted soils 

 devoted to onion culture. 



Downy-mildew, ^'"^' ^^^ blight {Pei^onospora schleideni Ung.). 

 — Close kin to the disastrous blight of potatoes, this disease 

 partakes of many of its characters, particularly in the rapidity 

 of its spread through an infested field. It may first be noted 

 on a small area of the field in which the tips appear as though 

 dashed with scalding water. Often under favorable climatic 

 conditions the affected areas increase many fold in a single 

 night, carrying complete destruction. 



It was first described in 1841 by Berkeley as "common 

 and destructive," and has long been known to onion growers 



